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March 17, 1964 P RQHDE 3,125,028

PUMP

Filed Jan. 25, 1960 4 Sheets-Sheet 2 IN VEN T OR.

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PUMP

Filed Jan. 25. 1960 4 Sheets-Sheet :5

IN VEN TOR.

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PUMP Filed Jan. 25, 1960 4 Sheets-Sheet 4 IN VEN TOR.

BY f akfi fa/fde United States Patent PUMP Robert P. Rohde, Saginaw, Mich, assignor to General Motors Corporation, Detroit, Mich, a corporation of Delaware Filed Jan. 25, 1960, Ser. No. 10,527 16 Claims. (Cl. 103-42) The invention relates to fluid pressure transmission devices, and more particularly pertains to regulatory means for fluid pressure generators of constant displacement.

In its most specific aspect, the invention is concerned with flow control means for constant displacement rotary pumps of the type finding application in power steering, especially of automotive vehicles. A pump of this type will be found described in the co-pending application of Philip B. Zeigler et 211., Serial No. 762,162, filed September 19, 1958. In such pump, the rate of fluid flow to the power steering gear is set by an orifice in the discharge conduit. This orifice is located downstream of a pressure-responsive valve controlling flow in a bypass conduit extending to the suction side of the pump. Thus, when a pressure drop develops across the orifice, the valve becomes displaced so that the fluid representing the excess over the requirements of the system is recycled.

The bypass valve of the prior application takes the form of a spring-loaded spool accommodated in a bore in the pump housing, the spring-loading being of the order of 7 lbs. For proper functioning of the valve, an extremely close fit is necessary between the spool and bore. The required fit is difficult to achieve in production and, as a consequence, when the valve is in closed position, there is usually some leakage about the CD. of the spool. Apart from this problem, it has been found that accumulation of dirt in the system may lead to sticking of the valve, a fault apparently due to the relatively light spring loading.

The present invention aims to provide a valve construction which overcomes the faults just indicated.

A further object is to provide a valve allowing for the use of a pump housing which contains relatively few drilled holes and which, as a consequence, may be manu factured at less cost.

Another object is to provide a bypass valve which does not react against the pump housing, greater flexibility in the selection of the housing material being thus permitted.

Still another object is to provide a valve having less throw, and which is therefore more responsive.

An additional object is to provide a bypass valve enabling a lower flow rate in the system when the system pressure is low.

Other objects and features of the invention will be apparent from the following description and the accompanying drawings illustrating preferred embodiments of the invention. In the drawings:

FIGURE 1 is a longitudinal sectional view of a pump construction incorporating the invention;

FIGURE 2 is a section on the line 22 in FIGURE 1;

FIGURE 3 is a section on the line 33 in FIGURE 1;

FIGURE 4 is a section on the line 44 in FIGURE 1;

FIGURE 5 is a section on the line 5-5 in FIGURE 1;

FIGURE 6 is a section on the line 6--6 in FIGURE 1;

FIGURE 7 is a view on the line 7--7 in FIGURE 2;

FIGURE 8 is a longitudinal sectional view showing a modification;

FIGURE 9 is a section on the line 9-9 in FIGURE 8;

FIGURE 10 is a section on the line Ill-10 in FIG- URE 8;

FIGURE 11 is a section on the line 11-11 in FIG- URE 8; and

FIGURE 12 is a section on the line 12-42 in FIG- URE 8.

Referring first to FIGURE 1, the numeral 10 denotes the pump housing which is a machined casting. This part is formed to provide a reservoir 12 receiving fluid from the system served by the pump via a port 14 (FIG. 3). A lid 16 overlying a seal 20 is secured by means of a bolt 18 threaded into the housing 10.

Within the reservoir 12 is a tube 22 serving in the conveyance of bypass fluid, as later explained. This tube is supported through a press fit in the housing 10 and communicates with a passage 24 in the housing (FIG. 2). At its feed end the tube 22 opens to a passage 26, in turn opening to the main cavity of the housing within which the principal parts of the pump are confined. These parts are arranged to provide an annular intake chamber 28 and include a thrust plate Stl, a cam ring 32 and a pressure plate 34, all comprising holes for the accommodation of aligning dowel pins 126.

Cam ring 32 encircles a rotor 38 carrying vanes 40 (FIG. 3), the rotor being splined to a drive shaft 42, turning in a bushing 44 and surrounded outward of the bushing by a seal 46. Such seal is accommodated in a recess formed in the boss portion 10a of the pump housing. The drive shaft 42 at the inner end thereof carries a snap ring 54 accommodated in an annular groove in the shaft and serving in the locating of the shaft relative to the rotor.

It will be understood that as the rotor turns, the vanes 40 are caused to reciprocate by the cam ring and that the consequent increase and decrease in the volume of the intervane chambers 50 provides a pumping action. Cam 32 is so formed that there are two opposed areas S of intake and two opposed areas D of discharge.

A closure plate 58 secured by a snap ring 60 sprung into an annular groove in the housing It) acts to axially locate and retain the parts inwardly thereof. Surrounding the closure plate 58 is a seal 62, also accommodated in an annular groove formed in the housing 10.

Thrust plate 36 (FIGS. 4 and 5) comprises re-entrant portions 64 extending radially inwardly of the inner periphery of cam ring 32 to provide intake ports. Pockets 66, 67 also comprised in such plate, which is formed with a recessed portion 36 (FIG. 5), receive fluid discharged by the intervane chambers 59. Holes 68 and 7t) serve purposes later explained.

In addition to the pockets 66, 67, plate 30 has therein arcuate pockets 72 which are open to the chambers 74 inward of the vanes 40. These arcuate pockets 72 find their complement in arcuate slots 76 (FIG. 2) and arcuate pockets 7 8 in pressure plate 34. In operation of the pump, pressure fluid derived from chamber 80 passes through slots 76 and holes 79 in pockets "i8 and is distributed via such slots and pockets together with the pockets 72 in plate 30 to the cavities 74 in which the vane slots terminate, thereby to pressure load the vanes radially outwardly against the cam ring 32. Pressure fluid enters the cavity 89 by means of openings 82 in the pressure plate 34 (FIG. 2). These openings (82) register with pockets 66 and 67 of the thrust plate 30 and communicate with such pockets via cross-over holes 73 in cam ring 32.

Pressure fluid received in the pocket 67 passes through hole 68 which registers with an orifice 88 located in the pump housing It This orifice is the flow'control orifice of the system and communicates via a passage 90 (FIG. 6) with the discharge port 92. A passage 94, communicating with the passage 90, opens to the previously mentioned hole 70 in the thrust plate 30 (FIG. 4). Such hole opens in turn to a hole 98 in the cam ring 32 (FIG. 3). The latter hole registers with a passage 100 in the pressure plate 34. Communication between the passage 100 and a chamber 102 delineated in part by the closure plate 58 is provided by an orifice 104 which is the pressure relief control orifice, as subsequently explained.

A passage 112 in the boss portion of housing 10 extends to a recess 114 in which the previously mentioned shaft seal 46 is accommodated. The passage 112 communicates with a radial slot 69 in plate 30. This slot 69 (FIG. 5) is open to the intake chamber 28. In addition to the passage 100 and the previously mentioned openings, holes and pockets provided in pressure plate 34, such plate has therein recesses 108 registering with the re-entrant portions 64 (FIG. 4) of the thrust plate 30. These recesses, like the re-entrant portions 64, communicate the intervane chambers 50 and the intake chamber 28 during the suction strokes of the vanes. With this arrangement, filling of such chambers from both sides of the cam ring 32 is provided for.

Pressure plate 34 further has therein radial passages 110 (FIGS. 1 and 2) opening to an annular chamber 113 from which the previously identified passage 24 extends (FIG. 2).

Chambers 80 and 102, above mentioned, are delineated by a diaphragm device 115 comprising a plate 116 secured to a ring of elastomeric material 118 formed as shown to allow for axial displacement of the plate. Ring 118 will be seen located between closure plate 58 and pressure plate 34. A metal band 119 L-shaped in crosssection is molded to ring 118 and is press-fitted over pressure plate 34.

With the arrangement as so far described and illustrated, it should be clear that in operation of the pump the chamber 80 is at all times filled with discharge fluid derived from upstream of the orifice 88, while chamber 102 is at all times filled with fluid derived from downstream of such orifice, the latter fluid, of course, being at system pressure.

Reverting to the diaphragm device 115, it will be seen that the plate 116 has a central aperture so that the same surrounds a valve element 130. The outer end of the valve element is threaded in the interest of a nut 132 whereby the plate and valve element are secured to each other.

Valve element 130 has a rounded portion 136 which normally rests on a seat provided by the pressure plate 34. This plate is formed with a central opening to accommodate the inner end of the valve element together with a Welch plug 138 and the inner end of the drive shaft 42.

A spring 140 biases the valve element 130 in the direction tending to maintain the rounded portion 136 seated as shown. Such spring reacts against the closure or cover plate 58 and is gauged to yield under a predetermined fluid pressure in chamber 80.

Within the valve element 130 is a ball relief valve 142, a seat for which 'is provided by a plug 144, made hollow so that the outer surface of the ball 142 is exposed to the fluid in the chamber 102. Ball 142 is loaded by a spring 146 surrounding a guide 148. The space 152 between the valve element 130 and the Welch plug 138 provides a dash-pot, which utilizes an orifice 150 and serves to prevent any tendency of the valve element to chatter in the operation of the pump.

In addition to the orifice 150, element 130 has therein a passage 154 opening to the bore in the pressure plate 34 accommodating such element. This bore, as previously noted, is open to the supercharge tube 22 via the pas sages 110, the annular chamber 113 and the passage 24.

The diaphragm, together with the valve element 130, constitutes a pressure-responsive control serving to bypass discharge fluid to the intake chamber when the quantity of the discharge fluid is in excess of that required to provide the desired flow rate. Ball relief valve 142, .on the other hand, serves to vent the system to the suction side of the pump whenever the system pressure becomes 4 excessive. Also, the latter valve plays a part in the flow control, as subsequently explained.

Operation In the operation of the pump, that portion of the discharge fluid which does not leave the pump through the flow control orifice 88 passes through the openings 82 in the pressure plate 34 into chamber 80. Some of this fluid is always derived from the pockets 66 in the thrust plate 30, such pocket, as aforestated, being in communication with the upper opening 82 through the upper crossover hole 73 in the cam ring 32. With the pump operating at high speed, discharge fluid entering the chamber is also derived from the pocket 67 in the thrust plate. This latter fluid follows the route of the lower cross-over hole 73 in the cam ring.

Whenever the output of the intervane chambers 50 exceeds the capacity of the orifice 88, a pressure drop, of course, develops across such orifice with a pressure buildup in the chamber 80. In the event this pressure buildup is sufficient to overcome the resistance of the spring 140 and the system pressure as reflected in the chamber 102 which, it will be remembered, communicates with the outlet passage via passages 94, 98 and 100, and the orifice 104 (FIG. 7) the diaphragm device flexes with opening of the valve 130. Thus, chamber 80 becomes open to the tube 22 through the central bore in the pressure plate 34, the radial passages 110 in such plate, the annular chamber 113 and the passage 24.

Tube 22 acts to supercharge the intake chamber 28 by the jet pump principal, the fluid entering the passage 26 from the mouth of the tube serving to draw fluid from the reservoir into such passage. On entering the intake cham ber 28, the velocity or" the fluid is translated into a static head assuring adequate filling of the intervane chambers and preventing cavitation, otherwise tending to occur under the bypass condition which corresponds to a condition of high speed operation of the pump.

Valve remains open for so long as the pressure in the chamber 80 is greater than the combined force of the spring and the pressure in the chamber 102. In this connection, it is to be observed that the diaphragm device 115 presents a greater area for fluid reaction in chamber 102 than in chamber 80, the difierential being due to the area of the seat for the valve 130.

As indicated in the forepart hereof, the pump herein is particularly contemplated for use in power steering. In such application, the orifice 88 may have a diameter calculated to provide a flow rate of 1.75 g.p.m., for example, at a system pressure of 1,000 lbs., taken as suflicient to actuate the steering linkage of the vehicle under parking conditions when steering resistance is maximum. With the values as indicated, the relief valve 142 is set to open at a predetermined pressure slightly greater than 1,000 lbs. p.s.i. Accordingly, when the pressure at 102 reaches the predetermined pressure, the valve 142 yields to communicate the chamber 102 and the intake chamber 28 via the radial bore 154 in the body of the valve 130, the central bore in the pressure plate 34, the radial passages 110 in such plate, the annular chamber 113, the passage 24, and the supercharge tube 22.

The flow rate through the passages 110 exceeds the flow rate into the chamber 102 from the system, this because of the restriction 104 (FIG. 7). As a consequence, the relief afforded by the valve 142 is followed by a secondary relief occasioned by the pressure drop in chamber 102. Thus, because of this pressure drop the pressure in the chamber 80 forces opening of the valve 130, allowing fluid to pass from the chamber 80 to the intake chamber by the route previously described.

The differential reaction areas above mention, provided by the seat for the valve 130, give a condition of relatively low flow rate through the system when the system pressure, i.e., the pressure at 102, is low. With the system pressure at 50 lbs. p.s.i., for example, as is approximately the case under cruising conditions when steering resistance and consequently the demand on the pump is low, and assuming that the area of the valve seat is /2 sq. in., the following obtains: 50 p.s.i. /2 sq. in.=25 pounds (differential, in favor of chamber 102). This is to be compared to the parking condition: 1000 p.s.i. /2 sq. in.=500 pounds (differential). It is thus seen that under the parking condition there is a greater force holding the valve 1319 closed than when the system pressure is lower. And, it should be further apparent that a larger pressure differential between chambers 86 and 1112 must consequently exist before valve 131) will open, allowing fluid to bypass to the suction part of the pump. Because the pressure drop through an orifice is determined by the flow rate through the orifice, it also follows, under the parking condition, that a greater flow rate through the orifice (88) must exist to create a larger pressure differential between chambers 811 and 102. Thus, in the case of the particular pump it has been determined that at a system pressure of 50 p.s.i. the flow rate to the system is about 1.50 g.p.m. as opposed to the 1.75 g.p.m. flow rate under the parking condition. The lower fiow rate at the lower system pressure is manifestly advantageous in that it translates into a lower system temperature and a reduction in the back pressure against which the pump works.

It will be understood that the force tending to effect displacement of the flow control valve (131?) must overcome not only the pressure of the fluid in chamber 1112 but also the resistance of the spring 1411. This spring serves to prevent premature displacement of the flow control valve at start-up and, with the. differential areas just discussed, sets the pressure unbalance at the desired value. It is preferred that the loading of the spring be of the order of 30 lbs, substantially four times that of the spring employed with the prior spool valve. Such loading, together with the rounded design of the valve 136), precludes any possibility of sticking of the valve.

Going now to FIGS. 8-12, illustrating a second form of the invention, there will be seen in FIG. 8 a housing member 160 having a boss portion 162 within which is confined a bushing 164 for the pump drive shaft 166. The housing 1611 mounts a reservoir 163 fastened to the housing 166 by means of a hollow bolt 170. Return fluid from the system served by the pump enters the reservoir via a fixture 172. A bafile 174 lessens turbulence within the reservoir.

Within the housing 162 will be seen a thrust plate 176, a cam ring 178, a pressure plate 1811 and a valve seat member 182. Outward of the latter member is a closure plate 184 formed to accommodate a fixture 186 through which fluid discharged by the pump passes to the system. The closure plate 184 is shown as secured in place by means of snap ring 190, received in an annular groove in the housing 16%).

As in the case of the embodiment first described, drive shaft 165 has a spline connection with the pump rotor 192. The latter carries vanes 1% which, in operation of the pump, are caused to reciprocate through contact with the inner periphery of the cam ring 178.

It will be observed that the inner end of the drive shaft 166 is accommodated in a recess formed in the pressure plate 18% and that outward axial displacement of the drive shaft is precluded by reason of a snap ring 1% carried by the shaft and abutting the rotor 192.

As shown in FIGURE 9, the thrust plate 176 is provided with pockets 200 for the reception of discharge fluid, and re-entrant portions 2-192 whereby intake fluid is allowed to enter the intervane chambers during the suction strokes of the vanes. Thus, the re-entrant portions 292 extend radially inwardly of the inner periphery of the cam ring 17 8 on the left side thereof.

In addition to the pockets 2%, the thrust plate 176 has therein arcuate pockets 2114 serving the same purpose as pockets '72 carried by the previously described thrust 6 plate 39 (FIG. 4). In other words, the arcuate pockets 2114- assist in the distribution of pressure fluid applied to load the vanes 194 radially outwardly to insure proper engagement thereof with the cam ring 178. Dowel pins 2% extend not only through the thrust plate 176, but also through the cam ring, the pressure plate 180 and the valve seat member 182 wherein they terminate.

From FIGURE 10, it will be noted that the cam ring 113 is provided with a pair of holes 210 communicating the pockets 2% of the thrust plate 176 and the openings 212 in the pressure plate (FIG. 11). Apart from the openings 212, pressure plate 189 has therein a pair or" arcuate slots 21 and a pair of arcuate pockets 216 in each of which is an opening 218. The pockets 216 are located in the inner face of the pressure plate. These slots, pockets and openings coact with the pockets 204 in the pressure loading of the vanes, the required fluid being derived through the two slots and the two openings.

The purpose of a slot 2211, seen in FIG. 11, will be later made clear.

The re-entrant portions 222 of the pressure plate register circumferentially with the re-entrant portions 222 of the thrust plate 176 and enable filling of the intervane chambers from the right side of the cam ring 178 (FIG. 8) during the suction strokes of the vanes. Just as in the case of the embodiment first herein described, the pump comprises an annular intake chamber 224 surrounding the cam ring.

A chamber 228 delineated by a diaphragm device 230 and the previously identified valve seat member 182 represents the source of the pressure fluid applied to load the vanes 194. The member 182 (FIG. 12) will be noted as having therein openings 232 communicating the openings 212 in the pressure plate 180 with the chamber 228 and openings 234 communicating such chamber with the slots 214 in the pressure plate. The numerals 232a and 234a denote recesses located in the inner face of the member 182 and extending to the edges of the openings 232 and 234, respectively.

A wide groove 236 in the valve seat member 182 extends generally radially from the central opening 238 therein to a point near the periphery of such member, where the groove registers with the previously mentioned opening 22% in the pressure plate 180.

The central opening 238 in the member 182 is dimensioned with relation to a valve element 240 having a rounded portion 242 which, in the normal position of the valve element, is disposed on a seat provided by the member 182. Valve element 2411 is secured to the previously mentioned diaphragm device 230 by means of a threaded collar 244 and is biased toward its shown position by a spring 246 reacted by the closure plate 184. Such element houses a piston relief valve 254 loaded by a spring 256.

The peripheral portion of the device 238 is formed to permit flexing of the device and is fitted between the valve seat member 182 and the closure plate 184. The device 2311 has therein a single opening 254 constituting the flow control orifice, setting the flow rate to the outlet chamber 252 and, hence, the flow rate to the system.

In the operation of the pump of FIGURES 812, all of the discharge fluid enters chamber 228 via the openings 232 in the valve seat member 182, these openings, as previously stated, being in registry with the openings 212 in the pressure plate 189. Pockets 2% in the thrust plate 176 serve to collect pressure fluid which is applied to balance the rotor in the axial direction against the pressure of the fluid in chamber 228.

That portion of the discharge fluid which goes to the system from the outlet cavity 252 enters such cavity through the flow control orifice 250, which may have a diameter corresponding to that of the flow control orifice in the pump first described herein.

When the valve 24% becomes displaced due to the development of the required pressure differential across the orifice 250, fluid passes from the cavity 228 to the intake chamber 224 via the route of the central bore of the valve seat member and the groove 23 in such member which groove, as aforestated, registers with the opening 220 in the pressure plate 1%. The width and depth of the groove and the area of the opening 22% are such as to provide a supercharging eflect, which is to say that the velocity of the fluid entering the intake chamber 224 from the opening 220 translates into a static head assuring thorough filling of the intervane chambers during the suction strokes of the vanes.

The piston relief valve 254 operates in a manner similar to the ball relief valve 142 (FIG. 1), that is, when the system pressure reaches a value exceeding the setting or" the spring 256, the piston valve yields to interconnect the outlet cavity 252 and the intake chamber 224, the interconnection being effected through a passage 26% in the body of the valve 24%. In this case, however, before valve 24% can become displaced to provide a secondary relief, the quantity of fluid flowing through valve 254 must be sufficient to bring about the required pressure drop across the diaphragm. Due to the greater diaphragm area available for reaction in the outlet chamber 252 as compared to chamber 223, the pump of FIGS. 8-12, just as the pump first described herein, may be readily flow-controlled to achieve a low flow rate at low system pressures with the advantages before indicated.

What is claimed is:

1. In a constant displacement pump of the type comprising an inlet passage and a flow control orifice through which discharge fluid passes, diaphragm means in which the orifice is located, means coacting with said diaphragm means to provide a pressure chamber at one side of said diaphragm means and upstream of said orifice, means coacting with said diaphragm means to provide an outlet chamber at the other side or" said diaphragm means, a valve element operatively connected with said diaphragm means, means providing a valve seat complementary to said element, the latter being displaced on the flexing of said diaphragm means to open said pressure chamber to said inlet passage and spring means tending to maintain said element on said seat.

2. In a constant displacement pump of the type com prising an intake chamber and a flow control orifice through which discharge fluid passes, diaphragm means in which the orifice is located, means coacting with said diaphragm means to provide a pressure chamber at one side of said diaphragm means and upstream of said orifice, means coacting with said diaphragm means to provide an outlet chamber at the other side of said diaphragm means, a valve element carried by said diaphragm means, a valve seat complementary to said element, said seat being provided by said means coacting with said diaphragm means to provide said pressure chamber, means communicating said pressure chamber and said intake chamber when said element is off said seat, and spring means disposed in said outlet chamber tending to maintain said element on said seat.

3. A pump as defined by claim 2 in which the area of said diaphragm means exposed to said outlet chamber is greater than the area thereof exposed to said pressure chamber, the diflerencce between said areas being set by the dimensions of said seat.

4. In a constant displacement rotary pump of the type comprising an intake chamber and a flow control orifice through which discharge fluid passes, diaphragm means in which the orifice is located, said diaphragm means carrying a valve element, a member spaced from said diaphragm means afiording a seat for said valve element, the space between said member and said diaphragm means serving as a pressure chamber, means communicating such space and said intake chamber when said valve element is oil its seat, a closure member forming an outlet chamber with said diaphragm means, and a spring within 8 said outlet chamber reacted by said closure member to normally maintain said valve element on its seat.

5. A constant displacement pump as defined by claim 4 where said valve element houses a relief valve displaceable to interconnect said chambers when the pressure in said outlet chamber reaches a predetermined value.

6. A constant displacement pump according to claim 5 in which the area of said diaphragm means exposed to said outlet chamber is greater than the area thereof exposed to said pressure chamber, the difference between said areas being set by the dimensions of said seat.

7. In a constant displacement pump of the type comprising an intake passage and a flow control orifice through which discharge fluid passes, diaphragm means delineating a first chamber at one side of said diaphragm means to contain pressure fluid derived from upstream of said orifice, means coacting with said diaphragm means to provide a second chamber at the other side of said diaphragm means to receive fluid passed by said orifice, a valve element carried by said diaphragm means centrally thereof, means providing a seat for said valve element, said valve element being displaceable on the flexing of said diaphragm means to open said first chamber to said intake passage, said valve element housing a relief valve displaceable to interconnect said chambers when the pressure in said second chamber reaches a predetermined value, and spring means tending to maintain said valve element on said seat.

8. In a constant displacement rotary pump comprising an intake chamber and a flow control orifice through which discharge fluid passes, a housing for the working parts of the pump, said flow control orifice being located in said housing, a pressure plate within said housing adjacent said working parts, diaphragm means delineating with said plate a first chamber within said housing at one side of said diaphragm means to contain pressure fluid derived from upstream of said orifice, a closure member outward of said plate and delineating with said diaphragm means a second chamber to receive fluid passed by said orifice, a valve element operatively connected with said diaphragm means, a seat for said valve element provided by said plate, said element being displaceable on the flexing of said diaphragm means to open said first chamber to said intake chamber, spring means tending to maintain said element on said seat, said spring means reacting against said closure member, the area of said diaphragm means exposed to said second chamber being greater than the area thereof exposed to said first chamber, the difference between said areas being set by the dimensions of said seat, and said valve element housing a relief valve displaceable to interconnect said chambers when the pressure in said second chamber reaches a predetermined value.

9. In a constant displacement type pump receiving fluid from an inlet passage and discharging the fluid under pressure through a flow control orifice to an outlet passage; fiow control means comprising diaphragm means, a first chamber at one side of said diaphragm means receiving fluid under pressure from upstream of said orifice, a second chamber at the opposite side of said diaphragm means receiving fluid under pressure from downstream of said orifice, a valve operatively connected to said diaphragm means, passage means including means providing a seat for said valve operatively connecting said first chamber to said inlet passage, spring means tending to urge said valve towards said seat, said valve being displaceable on the flexing of said diaphragm means to open said first chamber to said inlet passage when the pressure in one of said chambers is effective to overcome said spring means and the pressure in the other of said chambers, and said diaphragm means having an etfective area exposed to said other chamber larger than the effective area exposed to said one chamber so that said diaphragm means is effective to urge said valve towards said seat with a relatively low force when the pressures in said chambers, are

relatively low and with a higher force when the pressures in said chambers are higher whereby the pressure differential between said chambers effective to displace said valve from said seat varies between a low and a high pressure differential to provide a controlled rate of fluid flow through said orifice which varies in proportion to the pressure downstream of said orifice.

10. In a constant displacement variable speed driven pump for supplying a variable pressure system of the type comprising; an inlet passage, a discharge passage and an outlet passage for connection to a system; a pump receiving fluid from said inlet passage and discharging fluid to said discharge passage at different flow rates dependent on the speed at whch said pump is driven; flow control means connecting said pump discharge passage to said outlet passage and said pump inlet passage including a bypass passage connecting said discharge passage to said inlet passage, valve means controlling said bypass passage having an opened position opening said bypass passage and a closed position closing said bypass passage and including biasing means biasing said valve means to said closed position, orifice means connecting said discharge passage to said outlet passage, first fluid pressure actuator means having a first effective area operatively connected to said valve means and said output passage downstream of said orifice means and operative in response to fluid pressure downstream of said orifice means acting through said first effective area to move said valve means in a valve closing direction, second fluid pressure actuator means having a second effective area different from said first effective area operatively connected to said valve means and to said discharge passage means upstream of said orifice means and operative in response to fluid pressure upstream of said orifice means acting on said second effective area to move said valve means to an open position when the flow rate of discharge fluid from said pump to said outlet passage exceeds the capacity of said orifice to a degree suflicient to provide an increased pressure upstream of said orifice means and in said second fluid pressure actuator means to overcome the resistance of said biasing means and said first fluid pressure actuator means to provide flow control means for controlling the rate of fluid flow through said orifice means to said outlet passage to provide a rate of flow varying in proportion to increasing pressure in said outlet passage.

11. The invention defined in claim and said second effective area being smalier than said first effective area to provide an increasing rate of fluid flow through said orifice means to said outlet passage proportional to increasing pressure in said outlet passage.

12. The invention defined in claim 9 and a relief valve operative to connect said second chamber to said first chamber when the fluid pressure in said second chamber reaches a predetermined value.

13. The invention defined in claim 10 and said flow control means including a relief valve operative to connect said outlet passage downstream of said orifice means to said pump inlet passage when the fluid pressure in said outlet passage reaches a predetermined value.

14. The invention defined in claim 10 and said first and second fluid pressure actuator means including a chamber and a diaphragm dividing said chamber into first and second actuator chambers for said first and second fluid pressure actuator means respectively, said diaphragm being operatively connected to said valve means providing on one side said first effective area in said first actuator chamber and on the opposite side said second etfective area in said second actuator chamber with said first eifective area being larger than said second effective area to provide an increasing rate of fluid flow through said orifice means to said outlet passage proportional to increasing pressure in said outlet passage.

15. The invention defined in claim 10 and said pump having a pump housing and said orifice means being lo cated in said pump housing.

16. The invention defined in claim 14 and said orifice means being located in said diagram.

References Cited in the file of this patent UNITED STATES PATENTS 2,580,030 Lee Dec. 25, 1951 2,586,147 Caserta Feb. 19, 1952 2,683,418 Smith July 13, 1954 2,704,548 Ralston Mar. 22, 1955 2,713,556 Williams July 19, 1955 2,724,335 Eames Nov. 22, 1955 2,759,423 Keel Aug. 21, 1956 2,835,201 Pettibone May 20, 1958 2,858,766 Toschkoif Nov. 4, 1958 2,963,219 Palmqvist et al Dec. 6, 1960 2,996,013 Thompson et al Aug. 15, 1 961 

1. IN A CONSTANT DISPLACEMENT PUMP OF THE TYPE COMPRISING AN INLET PASSAGE AND A FLOW CONTROL ORIFICE THROUGH WHICH DISCHARGE FLUID PASSES, DIAPHRAGM MEANS IN WHICH THE ORIFICE IS LOCATED, MEANS COACTING WITH SAID DIAPHRAGM MEANS TO PROVIDE A PRESSURE CHAMBER AT ONE SIDE OF SAID DIAPHRAGM MEANS AND UPSTREAM OF SAID ORIFICE, MEANS COACTING WITH SAID DIAPHRAGM MEANS TO PROVIDE AN OUTLET CHAMBER AT THE OTHER SIDE OF SAID DIAPHRAGM MEANS, A VALVE ELEMENT OPERATIVELY CONNECTED WITH SAID DIAPHRAGM MEANS, MEANS PROVIDING A VALVE 